1. Field of the Invention
This disclosure relates to a sheet processing apparatus and an image forming apparatus.
2. Description of the Related Art
In the related art, an image forming apparatus such as a copier, a printer, a facsimile, and a multi-function printer includes a type provided with a sheet processing apparatus in a main body of the image forming apparatus and configured to perform processing such as binding or the like on sheets discharged from the main body of the image forming apparatus. Example of the sheet processing apparatus as described above includes a type configured to discharge a sheet discharged from the main body of the image forming apparatus once into a process tray, align the sheet with a sheet already stacked on the process tray, bind the sheets if needed in the process tray, and then discharge the processed sheets on a stacking tray as described in Japanese Patent Laid-Open No. 2003-128315.
FIGS. 13A and 13B are drawings illustrating a configuration of the sheet processing apparatus of the related art as described above. As illustrated in FIGS. 13A and 13B, a trailing end stopper 108 configured to stop and position the sheet(s) P is provided at an end of an intermediate processing tray 107. The sheet P discharged onto the intermediate processing tray 107 by a sheet discharge roller 103 is conveyed by an endless knurled belt 1161 configured to be rotated by the sheet discharge roller 103, and aligned at trailing ends thereof by abutting against the trailing end stopper 108.
The shape of the knurled belt 1161 is changed by an moving roller X.
That is, as illustrated in FIG. 13A, if there is no sheet bundle on the intermediate processing tray 107, the moving roller X does not move. In this case, the knurled belt 1161 is not deformed and rotates in a state of being in contact with the intermediate processing tray 107. In contrast, when a plurality of sheets P are stacked on the intermediate processing tray, the moving roller X moves to deform the shape of the knurled belt 1161 as illustrated in FIG. 13B, so that a pressure as constant as possible is applied from the knurled belt 1161 to a sheet bundle PA.
In the sheet processing apparatus of the related art as described above, when the knurled belt 1161 is deformed, the distance between the sheet discharge roller 103 and the moving roller X changes. Therefore, tensile force of the knurled belt 1161 is increased in comparison with the case where the number of stacked sheets is small.
When the tensile force is increased, a conveying force of the knurled belt 1161 increases correspondingly. When the conveying force is increased, the sheet P in abutment with the trailing end stopper 108 may be bent between the knurled belt 1161 and the trailing end stopper 108 and, consequently, alignment of the sheet may be impaired.
As a countermeasure, a method of controlling the amount of movement of the moving roller X by considering a change in tensile force of the knurled belt 1161 is conceivable. However, if the hardness of the knurled belt 1161 is changed by a change in atmospheric temperature or time degradation, a deviation occurs between the amount of movement of the moving roller X and the conveying force. This deviation is increased with increase in amount of movement. Accordingly, when an actual conveying force is smaller than a desired conveying force, the sheet P does not reach the trailing end stopper 108. In contrast, when the actual conveying force is larger than the desired conveying force, the sheet P is bent between the knurled belt 1161 and the trailing end stopper 108 and, consequently, alignment is impaired.